Area Forecast Discussion
Issued by NWS Wakefield, VA

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FXUS61 KAKQ 300125

Area Forecast Discussion
National Weather Service Wakefield VA
925 PM EDT Sat Apr 29 2017

Bermuda high pressure prevails off the Southeast Coast through the
Monday. A backdoor cold front will drop south across the northern
Delmarva peninsula tonight, then lifts back north as a warm front
Sunday. A cold front pushes across the region Monday night with high
pressure returning Tuesday.


920 pm update...Still very warm for late April across the
region, with many areas still around 80 degrees. Dew points in
the low 70s are also anomalously high for late April, making it
feel pretty uncomfortable. Skies are generally clear, with some
cirrus persisting. Think most areas will have a hard time
getting below 70 degrees tonight, and have raised mins a couple
degrees. Exception is lower MD Eastern Shore, where backdoor
cold front drops into the area later tonight, turning winds
onshore, and allowing temps to drop into the 60s. Otherwise,
forecast for tonight into Sunday in excellent shape.

Notable that CAPE values across the area this afternoon were in
the 4000-5000 j/kg range, which is extreme, and would normally
mean widespread thunderstorms across the region. However, strong
inversion around 850mb effectively capped the atmosphere, and
prevented thunderstorm development, except in the SW VA mtns.

Late afternoon discussion...Current wv imagery depicts a strong
mid/upper ridge centered over the sub-tropical wrn Atlantic,
with an active stream of convection on the nrn periphery of the
ridge from the Central Plains through the Ohio Valley. At the
surface, high pressure is co- located with the ridge aloft
offshore, with a stationary front from the Midwest to the
Northeast. Stratus from this morning along with a warm nose
~850mb has resulted in a rather strong cap this aftn, which has
hampered cu development despite a very unstable airmass.
Temperatures as of 19z average from the mid 80s to around 90,
with unusually high dewpoints (that are in record territory for
April) generally in the low 70s across the area.

A shortwave trough is expected to track across PA/NJ late this aftn
through the evening. This is expected to trigger iso/sct
showers/tstms as depicted in the HRRR over NE MD and the nrn
Delmarva mainly after 22z. Effective shear is progged to be 35-40kt
in this region, which could result in some locally strong tstms in
vicinity of an MLCAPE gradient over the Delmarva. MLCINH remains
rather high in this area, so any development of tstms over the Lower
MD Ern Shore will likely be conditional dependent on outflow from
the N. The shortwave trough will drag the stationary boundary swd as
a backdoor cold front late tonight. Mid-level instability persists
overnight with the potential for showers/tstms in vicinity of the
backdoor boundary. PoPs remain low ranging from 20-30%. Very mild
for late April with lows in the upper 60s to low 70s.


The front lifts back to the N as a warm front Sunday as
the upper ridge builds ahead of a trough digging across the Central
Plains. 850mb temperatures actually peak tonight and then drop back
to 14-16C by Sunday. Therefore, highs will be a few degrees lower
mid/upper 80s, but still well above normal. One exception will be
the Lower MD Ern Shore in vicinity of the boundary where highs should
be 5-10F lower than today. There is a lack of a trigger for
convection, so forecast PoPs area below 15%. Continued mild Sunday
night with lows in the mid/upper 60s.

A cold front approaches from the W Monday as the Central Plains
trough lifts into the Great Lakes. The front is expected to slow as
it pushes across the Appalachians with strong surface heating to the
lee of the mountains. Therefore, Pops should be slow to increase
through the aftn, and mainly over the Piedmont initially. The ridge
will hold strong along the coast with the ern half of the area
remaining dry through much of the day Monday. 500mb flow ahead of
the trough reaches 70-80kt, which yields 0-6km bulk shear ~50kt.
However, mid-level lapse rates are rather poor, which is limiting 0-
1km MLCAPE values of 500-600 J/kg once the strongest synoptic
forcing arrives locally (mainly 00-06z). The SPC Day 3 marginal risk
remains immediately W of the local area given some question as to how
unstable the thermodynamic profile will become. PW values ~1.5in
combined with strong forcing could result is some locally moderate
to heavy rain. The cold front crosses the region Monday night and
pushes offshore by 12z Tuesday. PoPs taper off from NW-SE from 06-
12z as drier air arrives from the NW. Highs Monday will generally be
80-85F with lows Monday night ranging from the upper 50s W to the
low/mid 60s along the coast. Breezy Monday with a SW wind ~15 mph
with gusts up to 25 mph.

A trough aloft builds over the Ern Conus Tuesday as surface high
pressure builds across the Southeast States. Temperatures will be
lower, but still on the warm-side of normal with highs ranging from
the mid 70s to near 80 under a mostly sunny sky. A wsw wind of 10-15
mph is expected with gusts up to 20-25 mph possible.


A secondary frontal boundary is expected to cross the
area Tuesday night and should bring cooler air to the
region. Isolated showers could occur north of the
Delmarva, however westerly winds aloft should provide
enough of a downsloping effect to keep the forecast dry
into Wednesday. Lows Tuesday night in the 50s (lower 60s
coastal SE VA/NE NC). Highs Wednesday in the mid-upper 70s
(upper 60s to lower 70s beaches) under mostly sunny skies
and sfc high pressure with light SW-W winds. Sfc high
slides offshore Wednesday night with lows in the
mid-upper 50s NW to lower 60s SE.

A warm front is expected to lift north across the area on
Thursday as low pressure develops along it Thursday night
into Friday. Increased clouds and precipitation chances
anticipated during this timeframe. SE winds become breezy
at the coast on Thu and become more S Thu night into Fri.
Overall, temperatures will be cooling with highs Thu/Fri
in the upper 60s NW to low-mid 70s SE. Lows Thu night in
the mid-upper 50s NW to lower 60s SE.


VFR conditions are expected to start the night with only a few
higher clouds moving into western portions of the region. High low
level moisture across the region will allow for the potential for
the potential of some patchy fog early on Sunday morning. Guidance
also continues to hint at marine air working into SBY overnight.
MVFR ceilings and visibilities will be possible at SBY. Conditions
should quickly improve back to VFR after 14Z. Light S/SW flow will
continue through the night and into Sunday with wind speeds of
generally 5-10 knots. Winds are expected to briefly turn to the E/SE
at SBY late tonight and into early tomorrow morning.

Outlook: MVFR stratus and visbilities will be possible once again
early Monday morning with a moist airmass in place. Conditions will
briefly return to VFR on Monday before a frontal boundary crosses
the region late in the day. This frontal boundary will bring the
potential for showers and thunderstorms along with sub-VFR
conditions. Dry/VFR conditions are expected through Wednesday with
potentially another system impacting the region Thursday.


Generally S-SW winds aob 15kt through Sunday night. Seas
average 2-4ft tonight; 2-3ft Sun/Sun night. Waves average

Low-end SCA conditions should begin for the Bay around
sunrise Monday morning when normal diurnal winds increase,
however speeds will continue to increase into the aftn as
the pressure gradient tightens substantially ahead of a
strong cold front which is approaching the region. All
waters should be within low-end SCA conditions by mid to
late Monday morning (S-SW 15-20kt/seas 3-5ft/waves 3-4ft)...
then solid SCA conditions by Monday aftn (15-25kt with
gusts to around 30kt Bay, Sound, ocean/seas average 5-7ft/
waves 4ft). Strong SCA winds persist ahead of/along the cold
frontal passage and then taper off rather quickly behind it
as winds become more westerly 15-20kt (gusts around 25kt
ocean). Seas may peak at 8ft in nrn coastal waters out near
20NM Monday night. SCA winds should end either by sunrise or
by mid morning on Tuesday. Wind speeds become more SW again
on Tue and remain breezy 10-15kt due to weaker cold air
advection occurring. Seas will be slower to subside, therefore
SCA flags should persist for the coastal waters through early
Tue aftn srn waters and as late as midnight Tuesday night nrn

Fairly benign conditions anticipated for Wed/Wed night with
high pressure over the area. Variable aob 10kt Wed/SE aob 15kt
Wed night. A warm front is expected to lift north across the
waters Thursday as low pressure develops along it Thursday
night into Friday. SE winds persist on Thu and become more S
Thu night into Fri. Wind speeds could increase to low-end SCA
(15-20kt) and seas could build to 5ft due to a tightening
pressure gradient. Will need to monitor the evolution of this
potential system.


Keeping flood advisory in Mecklenburg county going today, with
VDOT continuing to report numerous roads closed in the Kerr Dam
area, creating ongoing navigation concerns.


It still appears likely that Richmond and Norfolk will each end
the month with the warmest April on record. Very warm temperatures
expected today and an unseasonably warm April to date should combine
to push the April 2017 average temperature above that which occurred
in 1994. As noted below, both of the previous records on the books
were established in 1994. This month`s temperatures look to end up
around one degree above those values.

Average temperatures / Record Average Temperature
Through 4/28/17:

                APR 2017
                Avg temp  Record
Location        to date   Avg temp  Year
--------        --------  ------    ----
Richmond          63.1      63.2    1994
Norfolk           65.3      64.7    1994


Record high temps for today 4/29:
 RIC...93 in 1974
 ORF...92 IN 1974
 SBY...89 IN 1974
 ECG...90 IN 1974

Record high min temps for today 4/29:
 RIC...67 in 1956
 ORF...66 in 1981
 SBY...65 in 1974
 ECG...67 in 1981




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